Light emitting diode and method of manufacturing the same

ABSTRACT

Disclosed herein are a light emitting diode including a plurality of protrusions including zinc oxide and a method for manufacturing the same. According to an exemplary embodiment of the present disclosure, the light emitting diode includes: a substrate; a nitride light emitting structure disposed on the substrate; and a transparent electrode layer disposed on the nitride light emitting structure, wherein the transparent electrode layer includes a plurality of protrusions, the plurality of protrusions each have a lower portion and an upper portion, and a side of the lower portion and a side of the upper portion have different gradients.

PRIORITY CLAIMS AND CROSS-REFERENCE TO RELATED APPLICATION

This patent document is a continuation-in-part of, and claims priorityand the benefits of, a Patent Cooperation Treaty (PCT) applicationnumber PCT/KR2015/003959, entitled “LIGHT EMITTING DIODE ANDMANUFACTURING METHOD THEREFOR” and filed with the Korean IntellectualProperty Office (KIPO) on Apr. 21, 2015, which further claims priorityand benefits of Korean Application No. 10-2014-0048180, entitled “LIGHTEMITTING DIODE AND MANUFACTURING METHOD THEREFOR” and filed with theKorean Intellectual Property Office (KIPO) on Apr. 22, 2014, thecontents of which are incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to a light emitting diode and a methodfor manufacturing the same, which has a plurality of protrusionsincluding zinc oxide.

BACKGROUND

A light emitting diode converts electric energy into light energy. Thelight emitting diode can implement various colors by controlling acomposition ratio of compound semiconductor.

The light emitting diode emits energy corresponding to an energy gapbetween a conduction band and a valance band by a combination ofelectrons of an n layer and holes of a p layer when a forward voltage isapplied to the light emitting diode. The energy is mainly emitted in aheat or light form. In the case of the light emitting diode, the energyis emitted in the light form.

For example, nitride semiconductor has high thermal stability and wideband gap energy. As a result, the nitride semiconductor has receivedmuch attention in development fields of optical devices and high outputelectronic devices. In particular, a blue light emitting diode, a greenlight emitting diode, an ultraviolet (UV) light emitting diode, and thelike using the nitride semiconductor have been widely commercialized.

The existing nitride semiconductor has a problem of non-uniformity ofcurrent injection, low heat emission efficiency, low light emissionefficiency, etc. Therefore, to use the light emitting diode includingthe nitride semiconductor as a high efficiency light source, thetechnical development for maximum internal quantum efficiency, hightransparent ohmic electrode, and improvement in light extraction is veryimportant. Recently, many studies have been conducted on improvement inexternal quantum efficiency by improving the light extraction efficiencyrather than on improvement in the external quantum efficiency byimproving the internal quantum efficiency.

SUMMARY

Some implementations of the disclosed technology provide a lightemitting diode and a method for manufacturing the same capable ofimproving light extraction efficiency.

Some implementations of the disclosed technology provide a lightemitting diode and a method for manufacturing the same capable ofpreventing a surface of the light emitting diode from being damaged atthe time of forming a plurality of protrusions.

Some implementations of the disclosed technology provide a lightemitting diode and a method for manufacturing the same capable ofeffectively controlling a formation of a plurality of protrusions.

Some implementations of the disclosed technology provide a lightemitting diode and a method for manufacturing the same capable ofeffectively forming a plurality of protrusions by a simple process.

According to an exemplary embodiment of the present disclosure, a lightemitting diode is provided to include: a substrate; a nitride lightemitting structure disposed over the substrate; and a transparentelectrode layer disposed over the nitride light emitting structure,wherein the transparent electrode layer includes a plurality ofprotrusions, the plurality of protrusions each have a lower portion andan upper portion, and a side of the lower portion and a side of theupper portion have different gradients.

In some implementations, the transparent electrode layer can includezinc oxide.

In some implementations, the side of the lower portion included theplurality of protrusions can be a substantially vertical surface.

In some implementations, the side of the upper portion included theplurality of protrusions can have a gradient of 20 to 80° with respectto the substantially vertical surface.

In some implementations, the side of the upper portion included theplurality of protrusions can have a gradient continuously decreasing orincreasing with respect to the substantially vertical surface.

In some implementations, a horizontal width of the upper portionincluded the plurality of protrusions can be smaller than that of thelower portion.

In some implementations, the plurality of protrusions each can generallybe a disc shape or a hexagonal prism shape.

In some implementations, the nitride light emitting structure caninclude a first conductive type nitride semiconductor layer, an activelayer, and a second conductive type nitride semiconductor layer.

According to another exemplary embodiment of the present disclosure, amethod of manufacturing a light emitting diode is provided. The methodmay comprise forming a seed layer on a nitride light emitting structure;forming a mask pattern on the seed layer; forming a plurality ofprotrusions by re-growing the seed layer, wherein the plurality ofprotrusions each have a lower portion and an upper portion, and a sideof the lower portion and a side of the upper portion have differentgradients.

In some implementations, the seed layer and the plurality of protrusionscan form a transparent electrode.

In some implementations, the transparent electrode can include zincoxide.

In some implementations, the side of the lower portion can be asubstantially vertical surface.

In some implementations, the side of the upper portion can have agradient of 20 to 80° with respect to the substantially vertical side.

In some implementations, the upper portion has a horizontal widthsmaller than that of the lower portion.

In some implementations, the lower portion has a height same as athickness of the mask pattern.

In some implementations, the forming of the plurality of protrusions byre-growing the seed layer can include performing re-growing by ahydrothermal synthesis method.

In some implementations, the hydrothermal synthesis method can use amixed solution of zinc salt and hexamethylenetetramine.

In some implementations, the mask pattern can be formed using a lift-offtechnology.

In some implementations, the mask pattern can include oxides, nitrides,organic matters, or polymer.

In some implementations, the lift-off process can include forming a masklayer on a photoresist pattern and removing the photoresist pattern andthe mask layer can be formed using a thermal deposition method, anelectron beam deposition method, or a sputter deposition method.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating an exemplary lightemitting diode according to an exemplary embodiment of the presentdisclosure.

FIG. 2 is a flow chart illustrating a method for manufacturing anexemplary light emitting diode according to an exemplary embodiment ofthe present disclosure.

FIGS. 3 to 5 are cross-sectional views illustrating an exemplary lightemitting diode according to a method for manufacturing a light emittingdiode according to an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

Many research developments have been conducted to improve the lightextraction efficiency. Examples of the developments include changing asurface structure of the light emitting diode such as a surfaceroughness technology, a photonoic crystal structure technology, etc. Thesurface roughness technology includes a process of forming a roughnesspattern including a plurality of protrusions on the surface of the lightemitting diode using dry etching, wet etching, or the like.

As an example, Korean Patent No. 10-0568830 discloses a III-nitridesemiconductor light emitting device capable of increasing externalquantum efficiency of a light emitting device by forming protrusionshaving roughness on an exposed surface. According to the related art, aplurality of protrusions are formed on the exposed surface of theIII-nitride semiconductor light emitting device by using a dry etchingmethod including an ICP method, etc. However, due to the process offorming the plurality of protrusions by the dry etching method, thesurface of the light emitting diode can be damaged due to ionbombardment. Further, the process for forming the plurality ofprotrusions by the wet etching method is hard to control an etcheddegree when the surface of the light emitting diode is formed ofmaterials having properties very vulnerable to an acid.

Hereinafter, exemplary embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings. It isto be noted that in giving reference numerals to components of each ofthe accompanying drawing, like reference numerals refer to like elementseven though the like components are shown in different drawings.Further, in describing exemplary embodiments of the present disclosure,well-known functions or constructions will not be described in detailwhen it is determined that they can unnecessarily obscure the gist ofthe present disclosure. In addition, although exemplary embodiments ofthe present disclosure will be described below, the scope of the presentdisclosure is not limited thereto, but can be variously modified bythose skilled in the art.

FIG. 1 is a cross-sectional view illustrating an exemplary lightemitting diode according to an exemplary embodiment of the presentdisclosure.

Referring to FIG. 1, a light emitting diode includes a substrate 10, afirst conductive type nitride semiconductor layer 20, an active layer30, a second conductive type nitride semiconductor layer 40, a firstelectrode 60, a transparent electrode layer 80, and a second electrode90. The transparent electrode layer 80 includes protrusions 85.

The first conductive type nitride semiconductor layer 20, the activelayer 30, and the second conductive type nitride semiconductor layer 40can be sequentially disposed on the substrate 10. The first conductivetype nitride semiconductor layer 20, the active layer 30, and the secondconductive type nitride semiconductor layer 40 can form a nitride lightemitting structure. The first conductive type nitride semiconductorlayer 20, the active layer 30, and the second conductive type nitridesemiconductor layer 40 can be each made of or include galliumnitride-based compound semiconductor materials, that is, (Al, In, Ga)N.In particular, the active layer 30 has a composition element and acomposition ratio to emit light having a required wavelength, forexample, ultraviolet rays or blue light and the first conductive typenitride semiconductor layer 20 and the second conductive type nitridesemiconductor layer 40 can have a band gap greater than that of theactive layer 30.

Further, the first conductive type nitride semiconductor layer 20, theactive layer 30, and the second conductive type nitride semiconductorlayer 40 can be controllably or continuously grown using metal organicchemical vapor deposition (MOCVD), molecular beam epitaxy, hydride vaporphase epitaxy (HVPE) technologies, or the like. A thickness of a nitridelight emitting structure including the grown semiconductor layers 20,30, and 40 can range from 5 to 10 μm.

Here, the first conductive type nitride semiconductor layer 20 and thesecond conductive type nitride semiconductor layer 40 are an N type anda P type, respectively or vice versa. In the gallium nitride-basedcompound semiconductor layer, an N type semiconductor layer can beformed by doping impurities, for example, silicon (Si) and a P typesemiconductor layer can be formed by doping impurities, for example,magnesium (Mg).

The first conductive type nitride semiconductor layer 20 and/or a secondconductive type nitride semiconductor layer 40 can have a single layerstructure as described above, or a multi-layer structure. Further, theactive layer 30 can have a single quantum well structure or amulti-layer quantum well structure.

Further, a buffer layer (not illustrated) can be interposed between thesemiconductor layers 20, 30, and 40 and the substrate 10, prior toforming the first conductive type nitride semiconductor layer 20. Thebuffer layer can be formed to relieve a lattice mismatch between thesubstrate 10 and the first conductive type nitride semiconductor layer20 which will be formed thereon.

A transparent electrode layer 80 can be formed on the second conductivetype nitride semiconductor layer 40. The transparent electrode layer 80includes a plurality of protrusions 85. The transparent electrode layer80 and the plurality of protrusions 85 formed in the transparentelectrode layers 80 can include zinc oxide. The plurality of protrusions85 included in the transparent electrode layer 80 can be re-grown by ahydrothermal synthesis method which will be described below.

Each of the plurality of protrusions 85 can include a lower portion andan upper portion. A side of the lower portion and a side of the upperportion which are included in the protrusion 85 can have differentgradients. The side of the lower portion included in the protrusion 85can be a substantially vertical. In this case, the side of the lowerportion included in the protrusion 85 has no gradient with respect to asubstantially vertical surface._([NN1]) The substantially verticalsurface can mean a surface substantially vertical to a lower surface ofthe transparent electrode layer 80 or an upper surface of the secondconductive type nitride semiconductor layer 40. Further, the side of theupper portion included in the protrusion 85 can have a gradient of arange of 20 to 80° with respect to the substantially vertical surface. Ahorizontal width of the lower portion included in the protrusion 85 canbe smaller than that of the upper portion. That is, when the side of theupper portion has a gradient and the side of the lower portion is asubstantially vertical surface, the horizontal width of the upperportion included in the protrusion 85 can be smaller than that of thelower portion. When viewing the protrusion 85 from the top, theprotrusion 85 can be or include a circular shape or a polygonal shape.Further, the protrusion 85 can generally have a disc shape or apolygonal prism shape including a hexagonal prism shape. However, ashape of the protrusion 85 is not limited thereto and otherimplementations are also possible.

According to the exemplary embodiment of the present disclosure, whenviewing the protrusion 85 from the side, the lower portion is viewed asa rectangular shape and the upper portion is viewed as a triangularshape, but the shapes of the lower portion and the upper portionincluded in the protrusion 85 are not limited thereto and otherimplementations are also possible. Therefore, the upper portion of theprotrusion 85 can be or include a trapezoidal shape including a flatupper surface.

Further, the side of the upper portion included in the protrusion 85 canhave a gradient continuously increasing or decreasing with respect tothe substantially vertical surface. That is, although not illustrated,when the overall shape of the upper portion included in the protrusion85 has a semi-spherical shape, the side of the upper portion can havethe gradient continuously increasing with respect to the substantiallyvertical surface until the side of the upper portion reaches the topupper end area of the upper portion. However, the shape of theprotrusion 85 is not limited thereto but can include the case in whichat least a portion of the side of the upper portion included in theprotrusion 85 is a curved surface with respect to the substantiallyvertical surface.

The plurality of protrusions 85 can form a predetermined pattern. Theplurality of protrusions 85 can have the same crystal structure as thetransparent electrode layer 80.

The light emitting diode according to the exemplary embodiment of thepresent disclosure scatters light emitted from the active layer 30through the plurality of protrusions 85 included in the transparentelectrode layer 80, thereby improving the light extraction efficiency.

The first electrode 60 can be formed on one area of the first conductivetype nitride semiconductor layer 20. The second electrode 90 can bedisposed on one area of the transparent electrode layer 80. The firstelectrode 60 and the second electrode 90 are for supplying a current andwire bonding to the outside and can be made of or include Ti, Al, Cr,Ni, Au, Ag, Rd, or Ru or a combination of at least two thereof.

FIG. 2 is a flow chart illustrating a method for manufacturing anexemplary light emitting diode according to an exemplary embodiment ofthe present disclosure. FIGS. 3 to 5 are cross-sectional viewsillustrating an exemplary light emitting diode according to a method formanufacturing a light emitting diode.

Referring to FIG. 2, the method for manufacturing a light emitting diodeincludes forming a seed layer on a nitride light emitting structure(S10), forming a mask pattern on the seed layer (S30), and re-growingthe seed layer (S50).

In the forming of the seed layer on the nitride light emitting structure(S10), first, the first conductive type nitride semiconductor layer 20,the active layer 30, and the second conductive type nitridesemiconductor layer 40 are formed on the substrate. The nitride lightemitting structure can include the first conductive type nitridesemiconductor layer 20, the active layer 30, and the second conductivetype nitride semiconductor layer 40. The seed layer 50 can be formed onthe second conductive type nitride semiconductor layer 40. The seedlayer 50 can include zinc oxide (ZnO). The seed layer 50 can be formedby a deposition process or a coating process. In detail, a zinc oxidepowder can be evaporated to be deposited on the second conductive typenitride semiconductor layer 40 or can be directly coated on the secondconductive type nitride semiconductor layer 40 to form the seed layer50. Further, the seed layer 50 can be formed by a thermal depositionmethod, a pulsed laser deposition method, a thermal decompositionmethod, a spin coating method, a hydrothermal synthesis method, anorganic metal deposition method, or a vacuum deposition method using anelectronic beam.

In the forming of the mask pattern on the seed layer (S30), referring toFIG. 3, the mask pattern 70 can be formed on the seed layer 50. The maskpattern 70 can be formed by using a lift off technology. In someimplementations, the mask pattern 70 can be formed by a photolithographyprocess and a deposition process. For example, a mask layer is formed ona photoresist pattern on the seed layer 50 and the mask pattern 70 canbe formed by removing the photoresist pattern.

A portion of the seed layer 50 can be exposed between the respectivemasking elements of the mask pattern 70. Each masking element includedin the mask pattern 70 can have various shapes, in consideration of ashape and a size of the zinc oxide structure which will be re-grown onthe seed layer 50 of which a portion is exposed. Therefore, the area inwhich the seed layer 50 of the mask pattern 70 is exposed can have anisland pattern, etc.

In forming the mask pattern 70, the deposition process can performed byusing spin coating, a thermal deposition method, an electron beamevaporation method, a sputter deposition method, or the like. The maskpattern 70 can be formed of or include oxides, nitrides, organicmatters, or polymer. The mask pattern 70 can be formed of or includeAl₂O₃, MgO, NiO, ITO, or SiO₂.

In the re-growing of the seed layer (S50), referring to FIG. 4, theplurality of protrusions 85 can be formed by re-growing the seed layer50 of which the surface is not formed with the mask pattern 70. Theplurality of protrusions 85 can be grown by the hydrothermal synthesismethod. That is, when the seed layer 50 having the mask pattern 70formed on the surface thereof is dipped in an aqueous solution includingZn and O ions, the Zn and O ions can be adsorbed to the exposed seedlayer 50 to perform nucleation and growth. That is, the seed layer 50 ofwhich the surface is not formed with the mask pattern 70 can serve as aseed growing the plurality of protrusions 85. The plurality of grownprotrusions 85 can be grown along the crystal structure of the seedlayer 50.

A shape, a diameter, and a length of the plurality of protrusions 85 canbe controlled by changing conditions of temperature, time, an amount ofaqueous solution, a mole ratio, pH, etc., during the performance of thehydrothermal synthesis. Therefore, the protrusions 85 having variousdiameters, shapes, heights, etc., can be formed according to purpose.Further, the plurality of formed protrusions 85 can form a predeterminedpattern. Further, the hydrothermal synthesis aqueous solution includesdeionized water, zinc salt, and hexamethylenetetramine, in which a moleratio of the zinc salt and the hexamethylenetetramine can be kept at 2:1to 1:2. The hexamethylenetetramine serves as a catalyst to help a fastformation of the protrusions and can continuously supply OH— ion, etc.In addition to the hexamethylenetetramine, urea, ammonia, etc., can beused.

Further, among the hydrothermal synthesis aqueous solutions, a moleconcentration of the aqueous solution of the zinc salt and thehexamethylenetetramine can range from 0.0001M to 1M. When the moleconcentration is below 0.0001 M, it is difficult to control a content ofthe zinc salt and the protrusions 85 are not formed well and when themole concentration exceeds 1 M, source consumption amount for growingthe protrusions 85 is increased and thus it is difficult to control ashape and a size of the protrusions 85. The zinc salt can be zincnitrate hexahydrate.

Referring to FIG. 5, after the plurality of protrusions 85 aresufficiently grown between the mask patterns 70, the mask pattern 70 canbe removed. The protrusions 85 according to the exemplary embodiment ofthe present disclosure can be grown on the seed layer 50 exposed betweenthe mask patterns 70. The grown protrusions 85 and the seed layer 50form the transparent electrode layer. Therefore, according to the lightemitting diode and the method for manufacturing the same according tothe exemplary embodiment of the present disclosure, the protrusion 85pattern can be effectively formed on the surface of the light emittingdiode by the simple process without using the dry or wet etchingprocess. Therefore, the damage of the surface of the light emittingdiode can be prevented and the growth and the shape of the protrusions85 formed on the surface can be easily controlled. Further, the grownprotrusions 85 are combined with the seed layer 50 to form thetransparent electrode layer 85, and therefore the process is moresimplified and economical than the process of separately forming thetransparent electrode layer and then forming a fine pattern thereon.

The side of the lower portion and the side of the upper portion whichare included in each of the plurality of protrusions 85 and havedifferent gradients can be exposed by removing the mask pattern 70. Thatis, the lower portion of the protrusions 85 adjacently grown to the maskpattern 70 has the side which is the substantially vertical surface andthe upper portion of the protrusion 85 grown beyond the thickness of themask pattern 70 has an inclined side. That is, the height of the lowerportion of the protrusion 85 can depend on the thickness of the maskpattern 70.

The side of the upper portion of the protrusion 85 can have a gradientinclined inwardly. In this case, a horizontal width of the lower portionof the protrusion 85 can be greater than that of the upper portion.

Referring back to FIG. 1, after the mask pattern 70 is removed, thefirst electrode 60 can be formed on one area of the first nitridesemiconductor layer 20 and the second electrode 90 can be formed on onearea of the transparent electrode layer 80 on which the plurality ofprotrusions 85 are not formed.

The transparent electrode layer included in the light emitting diodeaccording to the exemplary embodiment of the present disclosure includesthe plurality of protrusions. Therefore, the scattering occurs in thetransparent electrode layer to improve the external extractionefficiency of light generated from the active layer.

According to the exemplary embodiment of the present disclosure, thelight emitting diode and the method for manufacturing the same canimprove the light extraction efficiency of the light emitting diode byforming the plurality of protrusions on the surface of the lightemitting diode.

According to the exemplary embodiment of the present disclosure, theplurality of protrusions are formed without using the dry etching methodor the wet etching method. Therefore, it is possible to prevent thesurface of the light emitting diode from being damaged and effectivelycontrol the formation of the plurality of protrusions even when thesurface of the light emitting diode includes the materials havingproperties vulnerable to the acid.

Further, according to the exemplary embodiment of the presentdisclosure, the light emitting diode and the method for manufacturingthe same can form the pattern including the plurality of protrusions onthe surface of the light emitting diode by the simple process, which iseconomical.

Various implementations of the present disclosure has been describedonly by way of example hereinabove, and the present disclosure can bevariously modified, altered, or substituted by those skilled in the artto which the present disclosure pertains without departing fromessential features of the present disclosure. Accordingly, the exemplaryembodiments disclosed in the present disclosure and the accompanyingdrawings do not limit the disclosed technology, and the scope of thepresent disclosure is not limited by the exemplary embodiments and theaccompanying drawings. The scope of the present disclosure should beinterpreted by the following claims, and it should be interpreted thatall the spirits equivalent to the following claims fall within the scopeof the present disclosure.

What is claimed is:
 1. A method of manufacturing a light emitting diode,comprising: forming a seed layer on a nitride light emitting structure;forming a mask pattern on the seed layer; forming a plurality ofprotrusions by re-growing the seed layer, wherein the plurality ofprotrusions each have a lower portion and an upper portion, and a sideof the lower portion and a side of the upper portion have differentgradients.
 2. The method of claim 1, wherein the seed layer and theplurality of protrusions form a transparent electrode.
 3. The method ofclaim 2, wherein the transparent electrode includes zinc oxide.
 4. Themethod of claim 1, wherein the side of the lower portion is asubstantially vertical.
 5. The method of claim 4, wherein the side ofthe upper portion has a gradient of 20 to 80° with respect to thesubstantially vertical side.
 6. The method of claim 1, wherein the upperportion has a horizontal width smaller than that of the lower portion.7. The method of claim 1, wherein the lower portion has a height same asa thickness of the mask pattern.
 8. The method of claim 1, wherein theforming of the plurality of protrusions by re-growing the seed layerincludes performing re-growing by a hydrothermal synthesis method. 9.The method of claim 8, wherein the hydrothermal synthesis method uses amixed solution of zinc salt and hexamethylenetetramine.
 10. The methodof claim 1, wherein the mask pattern is formed using a lift-offtechnology.
 11. The method of claim 10, wherein the mask patternincludes oxides, nitrides, organic matters, or polymer.
 12. The methodof claim 10, wherein the lift-off process includes forming a mask layeron a photoresist pattern and removing the photoresist pattern, and themask layer is formed using a thermal deposition method, an electron beamdeposition method, or a sputter deposition method.